This invention generally relates to a hand held electromechanical fastener driving tool, and more particularly to a unique vacuum return mechanism for resetting the tool to its restart configuration.
In the past such tools have used various combinations of cables and springs for returning the tool""s driving mechanism to its restart position after having driven a fastener into a work piece. For example see commonly owned U.S. Pat. No. 5,511,715, xe2x80x9cFlywheel Driven Fastener Driving Tool and Drive Unit,xe2x80x9d issued to Crutcher et al. Apr. 30, 1996.
Described and taught herein is a novel vacuum return mechanism, suitable for use in a hand held tool having a power drive cycle followed by a reset cycle whereby the tool mechanism is reset to the tools start configuration.
The vacuum return mechanism, as taught herein, comprises a cylinder having a piston assembly slidably received therein which is attached to the tool""s operating mechanism in such a way that as the tool progresses through its power cycle the piston assembly traverses through the cylinder creating a vacuum between the piston assembly and the sealed end of the cylinder opposite the piston assembly""s direction of travel. At the end of the tool"" power stroke, the vacuum between the piston assembly and the sealed end of the cylinder draws the piston assembly back towards the sealed end of the cylinder thereby resetting the piston and the tool""s operating mechanism to their appropriate restart position.
A novel structure is also taught whereby an accumulation of air between the piston assembly and the sealed end of the cylinder is permitted to bypass the piston assembly and be exhausted to the atmosphere, as the piston returns to its starting position.